The present invention generally pertains to injection molding of thin walled plastic products, and is particularly directed to the reduction of thermoplastic molding material consumption.
U.S. Pat. No. 3,944,124 to Hexel teaches a method of using flow channels and thin mold-cavity regions between such flow in a mold-cavity. The problem with such process is that heat is very quickly lost from the molten plastic molding material to the mold-cavity wall of the flow channels which extend for long distances and therefore the dimensions of the cross-sectional area of the flow channels have to be relatively large in order to optimize the process, and further heat is lost from the molten plastic molding material to the mold-cavity wall of the thin mold-cavity regions between the flow channels and therefore the mold-cavity thickness of the thin mold-cavity regions also has to be relatively large in order to provide enough heat to keep the molten thermoplastic molding material at a sufficiently high temperature required to maintain the molding material flowing. When the process of Hexel is optimized, the excessively large ribs formed by the flow channels cause the product to take up relatively much volume when stacked for transportation or storage.
U.S. Pat. No. 4,076,790 to Lind teach a process of inserting a film section into an opened mold-cavity, closing the mold-cavity to thereby enclose the film section in the closed mold-cavity, injecting plastic molding material into the mold-cavity, so that the plastic molding material covers and bonds to the film section and cooling the injected plastic material to form a product comprising a laminated wall section made up of the film section and molding material. The problem with such process is that the cavity thickness must be relatively thick in order to fill the full length of the molding cavity from the gate region to the edge defining region of the mold-cavity.